The present invention relates to a process for removing hydrogen cyanide from ethanedinitrile.
Ethanedinitrile, also known as dicyan, is a colourless and toxic gas which has a sweet pungent odour and a boiling point of −21° C. In chemical terms, its behaviour is similar to that of a halogen and it is therefore referred to as pseudohalogen. Ethanedinitrile is an important intermediate in the preparation of many commercial end products, for instance of synthetic fertilizers and nitriles. In addition, ethanedinitrile finds use in welding technology, since it burns with oxygen in the hottest known flame (4640 K). Further fields of use of ethanedinitrile are its use as a high-performance fuel, as a stabilizer in the preparation of nitrocellulose, or as a fumigant, especially in agriculture, for instance for killing parasites on agricultural soils or in the storage of goods (WO 2005/037332, U.S. Pat. No. 6,001,383).
Ethanedinitrile can be prepared in the laboratory by heating mercury(II) cyanide. In industry, it is usually obtained by oxidizing hydrogen cyanide, typically using chlorine over an activated silicon dioxide catalyst or nitrogen dioxide over copper salts. Alternatively, ethanedinitrile can be produced by catalytic oxidation of hydrogen cyanide with hydrogen peroxide in the presence of copper(II) and iron(II) salts, as described, for example, in DE 2 012 509, DE 2 022 454, DE 2 022 455 and DE 2 118 819.
Ethanedinitrile which has been obtained, for example, by one of the above methods by oxidizing hydrogen cyanide generally comprises unconverted hydrogen cyanide, and also by-products such as oxygen, carbon dioxide or water. The purification of ethanedinitrile, especially the selective and quantitative removal of hydrogen cyanide, is extremely demanding owing to the very similar chemical behaviour of ethanedinitrile and hydrogen cyanide.
U.S. Pat. No. 3,135,582 discloses a process for preparing ethanedinitrile by catalytic oxidation of hydrogen cyanide by means of oxygen and nitrogen oxides. This reaction forms, as a crude product, a mixture of ethanedinitrile, water, nitrogen monoxide, nitrogen dioxide, oxygen and hydrogen cyanide. Since some of these constituents have very similar melting and boiling points, it is difficult to obtain pure ethanedinitrile by simple condensation or distillation. The gaseous product mixture is therefore first contacted with an extraction solvent in which nitrogen dioxide and hydrogen cyanide are soluble, and nitrogen monoxide, oxygen and ethanedinitrile are simultaneously essentially insoluble. Ethanedinitrile is then obtained from the resulting gas mixture by condensation.
The yield of pure ethanedinitrile is relatively low in the process described in U.S. Pat. No. 3,135,582. Moreover, the complexity of an environmentally benign disposal of the hydrogen cyanide-containing extraction solvent is very high, especially since relatively large amounts of extraction solvent have to be used in order to guarantee complete removal of the hydrogen cyanide from the ethanedinitrile.
U.S. Pat. No. 4,073,862 discloses a process for removing ammonia, hydrogen sulphide and hydrogen cyanide from gases. In this process, the gas is first washed with a basic solution in order to remove hydrogen sulphide and hydrogen cyanide. The hydrogen sulphide is subsequently oxidized to elemental sulphur and removed, while the cyanide-containing basic solution has to be disposed of. Under these basic conditions, a hydrolysis of ethanedinitrile would, however, be unavoidable, and so the process described is unsuitable for the purification of ethanedinitrile.
It is therefore an object of the present invention to provide an environmentally benign and inexpensive process for removing hydrogen cyanide from ethanedinitrile, in which the yield of pure ethanedinitrile is at a maximum.
This object is achieved by the process according to claim 1. Further preferred embodiments are the subject-matter of the dependent claims.